Abstract. Environmental conditions have a strong influence on rates plant productivity and decomposition. In salt marshes, hydrology and salinity are important regulators of plant and soil processes, which, in turn, can influence the rate at which marsh ecosystems accumulate C and adjust to sea-level rise. For this study, we examined the influence of multivariate environmental conditions on belowground ingrowth (roots + rhizomes), decomposition and biomass in marshes dominated by Spartina alterniflora across two estuaries and a range of geomorphic settings. Secondly, we examined the influence of belowground plant biomass to soil C density, and C (labile and refractory) accumulation and accretion rates. Study locations occupied a full range of tidal elevations from below mean low water to above mean high water. Salinities ranged from 7–40, and soil properties also varied across marshes. While many of the environmental parameters were correlated across marshes, belowground ingrowth of S. alterniflora was negatively influenced by mean low water height, such that root growth increased with more drainage. Belowground decay rate increased with increasing salinity, but ultimately the percent of mass remaining was similar across marshes, averaging 59 ± 1 %. Above- and belowground biomass dynamics were estuary-dependent. In the coastal lagoon estuary, less flooding and a higher sedimentation rate favored above-and belowground biomass, which, in turn, increased soil C accumulation and accretion rates. Biomass dynamics in the coastal plain estuary, for the most part, were unrelated to environmental predictor variables, and had little influence on the accumulation of soil C or accretion rate. These findings indicate that mineral sedimentation is of utmost importance for promoting belowground biomass and soil C accumulation in sediment-limited systems while in minerogenic systems, belowground biomass may not scale with C accumulation and accretion, which may be influenced more by smaller submillimetre-sized C particles.
The effects of N, P and crude oil on the decomposition of Spartina alterniflora belowground biomass
